1. Field of the Invention
This invention relates to oligomers and higher homopolymers of meta- or para-isopropenyl-.alpha.,.alpha.-dimethylbenzylisocyanate and to a method of making same.
2. Description of the Prior Art
In U.S. patent application Ser. No. 400,799, filed July 22, 1982, now U.S. Pat. No. 4,439,616, there is disclosed a method for production of tertiary aralkyl isocyanates, such as tetramethyl xylylene diisocyanates (TMXDI), by thermal cracking of corresponding urethanes formed by addition to corresponding olefins of carbamic acid esters at moderate temperatures and in the presence of acid catalyst. Such process is particularly useful in producing the meta- and para-isomers of TMXDI and as the by-product thereof, substantial amounts of the corresponding meta-isopropenyl-.alpha.,.alpha.-dimethylbenzylisocyanate (m-TMI) and para-isopropenyl-.alpha.,.alpha.-dimethylbenzylisocyanate (p-TMI), respectively, are formed.
The m-TMI or p-TMI by-product in such systems may be recycled within the process to improve the overall yield of TMXDI therein, but has substantial utility per se as a separate product due to its difunctional character, viz., the presence of reactive isocyanato (--NCO) and isopropenyl groups. Thus, TMI may be homo- or co-polymerized to form polymers with isocyanate functionality which are cross-linkable with curatives containing a difunctional or polyfunctional amino or hydroxyl compound. Such cross-linkable compositions have film-forming properties and advantageously may be used for coatings as for example on metal, wood and glass substrates, as well as having potential applicability for production of molded articles, such as by reaction injection molding (RIM).
U.S. Pat. No. 3,290,350 discloses the polymerization of TMI by conventional methods using known addition polymerization initiators, such as those of the free radical type such as peroxy and azo initiators. More specifically, this patent discloses homopolymerization of m-TMI in solvent mixture with isooctane containing boron trifluoride etherate at a polymerization temperature of -73.degree. C. The resulting polymerized mixture then was allowed to equilibrate to room temperature and the polymer was isolated after three days. The isolated homopolymer had a softening temperature of about 60.degree. C. and a molecular weight of about 1500, being soluble in dimethylformamide and insoluble in xylene.
It is an object of the present invention to provide aromatic solvent-soluble linear oligomers or homopolymers of m-TMI or p-TMI.
It is another object of the invention to provide oligomers or homopolymers of m-TMI or p-TMI which are substantially free of cross-linking.
It is a further object of the invention to provide homopolymers of the above type which have substantially higher molecular weights than are achievable by the method of the prior art, e.g., on the order of 4,000 to 12,000 and higher.
It is a still further object of the invention to provide a method for making such oligomers or homopolymers, which does not result in diminution of reactive --NCO content when the homopolymer or oligomer is equilibrated at ambient temperature from sub-ambient reaction temperatures.
Other objects and advantages of the invention will be apparent from the ensuing disclosure and appended claims.